1. Field of the Invention
The present invention relates to a toner for developing latent electrostatic images formed by electrophotography, electrostatic recording, electrostatic printing, etc., method for producing the same, and apparatus for producing the same, and a developer, toner container, process cartridge, image forming method and image forming apparatus using such toner.
2. Description of the Related Art
The electrophotographic method generally contains a latent electrostatic image formation step in which a latent electrostatic image is formed on a photoconductor (hereinafter, also referred as a latent electrostatic image bearing member, image bearing member, electrophotographic photoconductor or the like) utilizing a photoconductive material by means of various means, a developing step in which the latent electrostatic image is developed with a toner so as to form a toner image, a transferring step in which the toner image is transferred to a recording medium such as paper, a fixing step in which the toner image transferred to the recording medium is fixed to the recording medium by heating, pressing, heating under pressure, applying a solvent vapor, or the like, a cleaning step in which the residual toner is removed from the photoconductor, and the like.
The developer for use in the electrophotography, electrostatic recording, electrostatic printing or the like is applied to an image bearing member such as a latent electrostatic image bearing member on which a latent electrostatic image is formed in the developing step, then transferred from the latent electrostatic image bearing member to a transfer medium such as a transfer paper in the transferring step. Thereafter, the developer is fixed onto a surface of the paper in the fixing step. As the developer for develop the latent electrostatic image formed on the latent electrostatic image bearing member, a two-component developer comprised of a carrier and a toner, and a single-component developer (e.g. a magnetic toner, and a non-magnetic toner) which does not require a carrier have been known in the art.
It has been required that the toner for use in the electrophotographic method is produced by a method which is energy-saving and has less adverse influence to the environment.
As a dry toner for use in the electrophotography, electrostatic recording or electrostatic printing, a pulverized toner has been widely used in the conventional art. Specifically, the pulverized toner is a toner formed by melt-kneading a binder resin such as a styrene resins or polyester resin together with other additives such as a colorant, and finely pulverizing the resulted mixture.
In the toner formation method using the pulverizing method, it is important to uniformly disperse each constituting materials and then pulverize in order to maintain the uniform shape of the resulted toner. Generally, the shape of the pulverized toner is uneven and the pulverized plane of the toner becomes random. Therefore, it is very difficult to control the shape or structure of the pulverized toner. Moreover, if the additives such as a colorant, a releasing agent, a charge controlling agent, and the like are added at a large quantity, the additives are prone to expose to the surface of the toner as the pulverization may occur at an interface between the additives and the binder resin at the time of the pulverization process. As a result, the charging becomes uneven between the toner particles, and there causes a problem such that the characteristics of the toner such as the flowability or charging ability are deteriorated.
Recently, the toner has been required to have a smaller particle size so as to realize a high quality image. However, the down sizing of the toner particle causes the following problems.    (1) The energy for the pulverization is exponentially increased.    (2) In addition to its uneven shape, the flowability of the toner is significantly lowered, and thus the supplying performance, transferring ability, and cleaning ability of the toner are deteriorated.    (3) The charging becomes significantly uneven between the toner particles, as a result of the pulverization at an interface between the additives and the binder resin.
Moreover, the toner production method using a chemical method has been recently studied. The chemical method is a method in which a toner is produced in a solvent, and specific examples thereof include a suspension-polymerization method, emulsified polymerization aggregation method, dissolution-suspension method, polyester elongation method, phase inversion emulsification method, and the like.
The suspension-polymerization method is such method that the additives, such as the colorant, releasing agent, charge controlling agent and the like, and the polymerization initiator are dispersed in monomers, the dispersion is then dispersed in an aqueous medium containing a dispersing agent so as to form oil droplets, and then the monomers within the droplet is polymerization reacted by heating so as to form a toner (refer to Journal of the Imaging Society of Japan, vol. 43, no. 1, pp. 33-39 (2004)).
One example of the emulsified polymerization aggregation method is a method described as follow. The polymerization initiator, styrene monomer and acryl monomer are added together so as to generate a resin emulsion as a result of the emulsification polymerization. The coloring agent dispersion and the resin emulsion, and optionally a dispersion of the other additives such as a releasing agent, charge controlling agent and the like are mixed, and added with a pH adjusting agent or aggregating agent so as to make them grow to have the predetermined particle size. Thereafter, fine particles are fused together by heating and stirring to thereby form a toner (refer to Japanese Patent (JP-B) No. 3141783, and Journal of the Imaging Society of Japan, vol. 43, no. 1, pp. 40-47 (2004)).
The dissolution suspension method is a method which involves a volume contraction, and includes a step for suspending, in an aqueous phase, an oil phase formed by dissolving a binder resin in an organic solvent capable of dissolving the binder resin so as to prepare suspension, and a step of removing the organic solvent from the suspension. In this method, additives such as a colorant, releasing agent, charging agent and the likes are dispersed or dissolved together with the binder resin in a volatile solvent such as an organic solvent having a low boiling point, this solution is then suspended in an aqueous medium in the presence of a dispersant so as to form oil droplets, and the volatile solvent is removed from the oil droplets. Therefore, the dissolution suspension method is superior to the suspension polymerization method, emulsified polymerization aggregation method or the like, as the wide selection of resin is usable for the binder resin, and particularly, polyester resin effective in a full-color process which requires clearness or smoothness of an image area after fixing can be used (refer to JP-A No. 07-152202, and Journal of the Imaging Society of Japan, vol. 43, no. 1, pp. 48-53 (2004)).
The polyester elongation method is a method which includes a step for emulsifying and aggregating an oil phase in an aqueous phase so as to form dispersion wherein the oil phase is formed by dissolving polyester resin containing a reactive resin in an organic solvent capable of dissolving the polyester resin, and a step for allowing the polyester to elongation reaction while removing the organic solvent from the dispersion. Unlike the suspension polymerization method and emulsified polymerization aggregation method, this method is superior in terms of that polyester resin effective in a full-color process which requires clearness or smoothness of an image area after fixing can be used, and viscoelasticity of a toner can be controlled by controlling the elongation reaction, resulting the fixing ability at a wide range of temperature (refer to Journal of the Imaging Society of Japan, vol. 43, no. 1, pp. 54-59 (2004)).
The phase inversion emulsification method is such a method that additives such as a colorant, releasing agent, charging agent and the like are dispersed or dissolved together with a binder resin in a volatile solvent such as an organic solvent having a low boiling point, a continuous aqueous phase is poured into the thus obtained solution so as to inverse from W/O (water in oil) dispersion to O/W (oil in water) dispersion to thereby form oil droplets, and the volatile solvent is removed from the oil droplets. This method is also notable as the wide selection of resin is usable for the binder resin, and particularly, polyester resin effective in a full-color process which requires clearness or smoothness of an image area after fixing can be used (refer to JP-B No. 3063269, and JP-A No. 08-211655).
As a toner produced in accordance with such the chemical method, there haven been known a capsule toner, core-shell toner and the like, which have embodiments capable of effectively exhibiting the predetermined functions in view of the recent concerns about the environmental issues.
Comparing to the pulverizing method, the chemical method produces toner having a smaller particle size and a narrower particle size distribution. However, in accordance with the chemical method, the toner is produced in water or a hydrophilic solvent, and thus the surface of the resulted toner becomes hydrophilic, which causes the lowered charging ability, and unstability in the storage stability and environmental characteristics, and induces problems such as inferior developing and transferring, toner scattering, lower image quality, and the like. Moreover, as the chemical method releases a large volume of waste liquid and requires a large amount of energy to dry the toner, it is not preferable in view of the environmental load.
In order to prevent deterioration of flowability, transferring property or cleaning property due to the down-sized toner in the pulverization method and to prevent lowering of charging ability, and unstability of storage stability and environmental characteristics due to the hydrophilic surface of the toner in the chemical method, the conventional toner is generally added with inorganic or organic fine particles on the surface thereof, and the adhesion of the toner is reduced by the effects of the fine particles. Moreover, the inorganic or organic fine particles are generally applied to the surface of the toner also for the purpose of applying sufficient flowability enough to transfer the toner from the toner vessel to the developing unit.
As such the fine particles, there have been known hydrophobic powder such as hydrophobic silica (refer to JP-A No. 52-30437), a mixture wherein aluminum oxide or titanium oxide fine particles are added to silica fine particles (refer to JP-A No. 60-238847), aluminum-coated titanium fine particles (refer to JP-A No. 57-079961). Moreover, as the titanium oxide, there have been proposed the one having a crystal structure of anatase (refer to JP-A No. 60-112052), aluminum oxide-coated titanium oxide (refer to JP-A No. 57-79961), and titanium oxide fine particles which are surface treated with a coupling agent (refer to JP-A No. 04-40467). However, silica, which has the highest effect on providing flowability, is commonly used. By applying hydrophobic powder such as silica, the flowability, developing performance and transferring performance of the toner is largely improved.
However, theses external additives applied on the surface of the toner continuously receive physical stress in the developing unit, transferring unit, cleaning unit, or the like at the time being used in a copying machine or printer. As a result, the external additives may be buried into the toner inside from the surface thereof, or be detached from the surface of the toner. Therefore, the adhesion of the toner increases with time, which causes the decrease in the transferring efficiency and reliability of cleaning.
As a toner production method which replaces the pulverization method or chemical method, there has been proposed a method in which fine droplets are formed by utilizing piezoelectric pulse, and the droplets are dried and solidified so as to form a toner (refer to JP-A No. 2003-262976). Moreover, there has proposed a method in which droplets are formed by utilizing heat expansion inside of a liquid room, and the droplets are dried and solidified so as to form a toner (refer to JP-A No. 2003-280236). Furthermore, there has been proposed a method in which acoustic lens are used to carry out the same process mentioned above (refer to JP-A No. 2003-262977).
The toner produced in accordance with any of these methods is also added with the charge controlling agent so as to provide charge controlling effect which is the important characteristic of the toner. In the case where the toner dispersion added with the charge controlling agent is ejected from fine ejection holes, it is difficult to stably eject the dispersion without clogging the ejection holes in most cases. Therefore, such the method requires a process for finely dispersing the charge controlling agent, and may further requires an addition of a dispersion stabilizer so as to maintain the finely dispersed state at a certain period. Especially when an aqueous medium is used and fine droplets are dried and solidified to thereby produce a toner, a surface of the resulted toner becomes hydrophilic. In such the case, similarly to the case of the pulverization method and chemical method, it is necessary to add inorganic or organic fine particle to the surface of the toner so as to prevent the reduction in the charging ability, and unstability in the storage stability and environmental characteristics.
In recent years, the dry toner has been required to realize an image of the quality close to offset printing or a photograph. To this end, as well as the down sizing the toner so as to attain high resolution, it is desired that the deposition about of the toner is reduced and a pile height of the toner layer is lowered so as to provide a natural texture like the one obtained with the offset printing, and clearness of the colorant is increased so as to widen the capacity of the color reproduction.
In order to balance between the reduced amount of toner deposition, lowered pile height of the toner layer, and remaining of the high image density, it is a common practice that the amount of the pigment to be contained in the toner is increased. If the amount of the pigment is increased, however, the large amount of the pigment may inhibit the fixing, or the charge of the toner may become unstable as the pigment is present on the surface of the toner, which may cause the deterioration of the image. In the case of the chemical toner, such as the one obtained from the suspension polymerization method or dissolution suspension method, it is difficult to form droplets and obtain particles as the viscosity of the solution is increased.
In order to improve the clearness of the colorant so as to widen the capacity of color reproduction, there have been known the method in which a pigment is finely dispersed, and the method in which a dye is used.
As the technique for finely dispersing the pigment, especially for the purpose of stabilizing the dispersion state in the organic solvent, JP-A No. 2005-232443 discloses the use of graft polymer pigment dispersant, and JP-A No. 2005-36220 discloses the use of silicone macromer pigment dispersant. If the pigment is dispersed more finely, the larger amount of the pigment dispersant is required to stabilize the dispersion. This cases problems such that the charging stability of the toner is inhibited, the fixing property is largely changed, and the like. As the technique for finely pulverizing the pigment, the use of a ball mill or beads mill is commonly known. In recent years, in order to even more finely pulverize the pigment, there have been proposed the pulverization method using a laser ablation (refer to JP-A Nos. 2004-267918 and 2005-238342), the pigment fine dispersion method using the dissolution and precipitation process (refer to JP-A Nos. 2004-331946, 2004-091560 and 2006-193681), and the method in which the pigment solution is spray-dried to provide fine particles of the pigment (refer to JP-A No. 2005-518278 and 2006-152103). However, the large amount of the pigment dispersant is necessary to stabilize the dispersion, and there are sill the problems such that charging stability of the toner is inhibited, the fixing property is largely changed, and the like.
The dye is excellent in color tone and clearness. However, it also has problems such that the light fastness is poor, the formed image is blurred as the dye is migrated during the storage, and a film or the like is stained if the image formed with the dye is contacted with the film or the like. In order to solve these problems, there has been proposed the use of polymer dye. Examples thereof are a polymer dye in which a phenol dye is introduced into polyester structure (refer to JP-A No. 62-245268), a polymer dye in which an azo dye having a vinyl group is polymerized (refer to JP-A No. 63-85644), a polymer dye added with a rhodamine dye (refer to JP-A Nos. 01-147472, 01-147476, 01-161362, 01-161363, 01-161364, 01-161365, 01-164956, 01-164957, 01-164958, 01-164959, 01-173056, 01-173057, 01-173058, 01-173059, 01-173060, 01-173064, 01-173065, 01-173066, 01-173067, 01-173068, and 02-2575). However, these polymer dyes are all unique and expensive.
Moreover, there have been proposed the toner for latent electrostatic photography containing a colorant obtained by reacting the resin having a carboxyl group or sulfonyl group at a side chain thereof with a basic dye (refer to JP-B No. 3068654), and color particles and a color toner in which the amount of the functional groups of the resin and reactive amount of the dye to the resin are determined. However, these are similar to the toner in the related art in terms of a particle size distribution and characteristics of the toner.
There has been also proposed a toner production method in which a toner composition fluid in which a toner composition is made into liquid is ejected from ejection holes of a nozzle by applying pressure to the toner composition fluid so as to form a column state of the toner composition fluid, and the toner composition fluid is made into droplets by vibrating a nozzle plate or retention means at a constant frequency (refer to JP-A Nos. 2006-293320, and 2007-108731). In this method, a pigment used as a colorant is finely dispersed, and thus the capacity of color reproduction is not necessarily wide, as well as having problems of clogging or unstable ejection due to the pigment.
As mentioned above, it is the current situation that there have not yet been provided a method for producing a toner, the toner produced by the same, and an image forming method using such the toner, all of which have sufficient performances such that the resulted toner has a wide capacity of color reproduction, vivid color tone, high clearness, sharp particle size distribution, and excellent toner characteristics such as charging ability, environmental stability, storage stability and the like, does not generate any waste liquid, does not contain any residual monomer, does not require drying process, and is at low cost.